1. Field of the Invention
This invention is directed to a method and device for decontaminating high concentrations of bacterial bioaerosols, viral bioaerosols and other airborne microorganisms in flight at high flow rates. The invention is particularly applicable to the Heating, Ventilation and Air Conditioning (HVAC) industry and bioterrorism defense industry.
2. Description of the Related Technology
The escalating threat of airborne biologic and bioterrorism agents, present a need for robust technologies and methods to mitigate the spread of airborne contaminants. Events such as the avian flu pandemic, the 1976 Legionnaires outbreak in Philadelphia and the 2001 anthrax terrorism in the United States demonstrate the ability to rapidly spread biologic contaminants through ventilation systems.
To address these concerns, scientists are focusing on non-thermal plasma-based technologies, which have previously proven successful in deactivating microorganisms, such as viruses and bacteria, in solution and on surfaces. Plasma has proven to be useful as a microbial disinfectant in many surface sterilization studies and it can be delivered with low power consumption, as a non-thermal discharge that is relatively easy to construct requiring simple power supplies.
Decontamination of microorganisms in flight using non-thermal plasma technology, however, has not been effectively implemented. Plasma-based air decontamination has only been found effective when coupled with high efficiency particulate air (HEPA) filters, which trap and kill microorganisms. HEPA filters, however, are inefficient at trapping submicron-sized airborne microorganisms. Moreover, HEPA filters also cause significant pressure losses in heating, ventilation, and air conditioning (HVAC) systems, generating high energy and maintenance costs. The filters function as a surface on which contaminants are captured; therefore, the prior art methodologies are, in essence, the same as standard plasma surface sterilization. Numerous technologies, such as those disclosed in Chinese Patent no. 02655913Y, U.S. Patent application publication no. 2004/0037736A1 and International patent application publication nos. WO 03/063914 A2, WO 05/067984 and WO 06/003382 A1, similarly sterilize air by directing plasma emissions at a filter surface, which entraps the biologic contaminants.
Apart from treatments in solution or on surface, there remains a need to develop a means for in flight plasma-based decontamination so as to be able to deactivate microorganisms in the air while in motion. This may be particularly useful for sterilizing ventilation systems and preventing the spread of airborne biologic agents.
In Michael J. Gallagher, et. al., “Non-Thermal Plasma Applications in Air-Sterilization,” International Symposium on Plasma Science (August 2005), a non-thermal plasma emission device and method for treating airborne biologic contaminants was proposed, but neither tested nor sufficiently described such that one of ordinary skill in the art would be able to reproduce the proposed technology and in flight plasma sterilization methodology. The publication discloses a calibration test using a Pathogen Detection and Remediation Facility (PDRF) incorporating a plasma emission device such as a Dielectric Barrier Discharge (DBD) device or a Magnetically-Rotated Gliding Arc (MRGA) device. The calibration experiment involved emission of cyanobacterial aerosol to identify bioaerosol losses from diffusion, inertia and evaporation to establish accurate controls before applying non-thermal plasma. Additionally, the publication proposes, but does not describe, sterilization experiments with cyanobacteria and influenza A virus. The publication does not apply plasma to the cyanobacteria calibration experiments.
Based on the known efficiency of plasma-based sterilization technology, it is unexpected that it would be possible to render a substantial proportion of biologic agents inactive in flight in a short time, such as milliseconds, using non-thermal plasma. By comparison, DBD surface sterilization treatment times are often 1000 times longer, on the order of seconds, and in some cases even minutes in duration.
Therefore it would be desirable to develop a method capable of efficiently sterilizing airborne biologic agents within a period of milliseconds.